回答此问题可获得 20 贡献值,回答如果被采纳可获得 50 分。
<p>我将要破解Python导入系统。假设我们有以下目录结构:</p>
<pre><code>.
├── main
│ ├── main.py
│ └── parent
│ └── __init__.py
└── pkg1
├── __init__.py
├── sub
│ ├── __init__.py
│ └── import_global.py
└── success.py
</code></pre>
<p>启动脚本将是<code>main.py</code>,因此应该有一个最顶层的模块<code>parent</code>。现在,我想模拟一个子包,它的全名是<code>parent.intermediate.pkg1</code>,它确实引用了<code>pkg1</code>目录。在</p>
<p>实际上不存在<code>intermediate</code>模块,但是,我确实需要模拟一个模块(在我的实际项目中,这个中间模块的名称将动态生成)。所以我决定使用Python导入钩子。在</p>
<p>首先,让我介绍一下<code>pkg1</code>的内容。在</p>
<p>包装1/分包/进口_全局.py公司名称:</p>
^{pr2}$
<p>包装1/成功.py公司名称:</p>
<pre><code>Value = 'Success'
</code></pre>
<p>和(部分主.py),我做了一些测试用例:</p>
<pre><code>class MainTestCase(unittest.TestCase):
def test_success(self):
from parent.intermediate.pkg1 import success
self.assertEqual(success.Value, "Success")
def test_import_global(self):
from parent.intermediate.pkg1.sub import import_global
self.assertEqual(import_global.Value, 3)
def test_not_found(self):
def F():
from parent.intermediate.pkg1 import not_found
self.assertRaises(ImportError, F)
unittest.main()
</code></pre>
<p>所有的<code>__init__.py</code>都是空的。现在它将实现导入钩子。我起草了两个版本,每个版本都有一些问题。在</p>
<p>第一版:</p>
<pre><code>class PkgLoader(object):
def install(self):
sys.meta_path[:] = [x for x in sys.meta_path if self != x] + [self]
def find_module(self, fullname, path=None):
if fullname.startswith('parent.'):
return self
def load_module(self, fullname):
if fullname in sys.modules:
return sys.modules[fullname]
parts = fullname.split('.')[1:]
path = os.path.join(os.path.dirname(__file__), '..')
# intermediate module
m = None
ns = 'parent.intermediate'
if ns in sys.modules:
m = sys.modules[ns]
elif parts[0] == 'intermediate':
m = imp.new_module(ns)
m.__name__ = ns
m.__path__ = [ns]
m.__package__ = '.'.join(ns.rsplit('.', 1)[:-1])
else:
raise ImportError("Module %s not found." % fullname)
# submodules
for p in parts[1:]:
ns = '%s.%s' % (ns, p)
fp, filename, options = imp.find_module(p, [path])
if ns in sys.modules:
m = sys.modules[ns]
else:
m = imp.load_module(ns, fp, filename, options)
sys.modules[ns] = m
path = filename
return m
loader = PkgLoader()
loader.install()
</code></pre>
<p>如果<code>test_import_global</code>失败:</p>
<pre><code>E..
======================================================================
ERROR: test_import_global (__main__.MainTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
File "main.py", line 54, in test_import_global
from parent.intermediate.pkg1.sub import import_global
File "main.py", line 39, in load_module
m = imp.load_module(ns, fp, filename, options)
File "../pkg1/sub/import_global.py", line 1, in <module>
from operator import add
File "main.py", line 35, in load_module
fp, filename, options = imp.find_module(p, [path])
ImportError: No module named operator
----------------------------------------------------------------------
Ran 3 tests in 0.005s
FAILED (errors=1)
</code></pre>
<p>现在对于第二个版本,我修改了<code>load_module</code>:</p>
<pre><code>def load_module(self, fullname):
if fullname in sys.modules:
return sys.modules[fullname]
parts = fullname.split('.')[1:]
path = os.path.join(os.path.dirname(__file__), '..')
# intermediate module
m = None
ns = 'parent.intermediate'
if ns in sys.modules:
m = sys.modules[ns]
elif parts[0] == 'intermediate':
m = imp.new_module(ns)
m.__name__ = ns
m.__path__ = [ns]
m.__package__ = '.'.join(ns.rsplit('.', 1)[:-1])
else:
raise ImportError("Module %s not found." % fullname)
# submodules
for p in parts[1:]:
ns = '%s.%s' % (ns, p)
# ======> The modification starts here <======
try:
fp, filename, options = imp.find_module(p, [path])
except ImportError:
return None
# ======> The modification ends here <======
if ns in sys.modules:
m = sys.modules[ns]
else:
m = imp.load_module(ns, fp, filename, options)
sys.modules[ns] = m
path = filename
return m
</code></pre>
<p>如果<code>test_not_found</code>失败:</p>
<pre><code>.F.
======================================================================
FAIL: test_not_found (__main__.MainTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
File "main.py", line 65, in test_not_found
self.assertRaises(ImportError, F)
AssertionError: ImportError not raised
----------------------------------------------------------------------
Ran 3 tests in 0.004s
FAILED (failures=1)
</code></pre>
<p>所以问题现在很清楚了:如何实现import钩子,以便这三个测试用例都能通过?在</p>